Vickers 40mm. "S" Gun

A Vickers 40mm. "S" Gun with Littlejohn adaptor

3lb AP shot beside a Littlejohn round

At the outbreak of war the standard Royal Air force aircraft carried an armament consisting of .303 machine guns, by the Summer of 1940 the 20mm Hispano cannon had started to come into use and the question of using the guns against tanks was raised, armour piercing ammunition was developed but it was clear that a more substantial gun would be required. The result was a 40mm gun developed by Vickers, trials in a Hurricane aircraft had begun by the end of the year, this was known as the Hurricane IID and production started in Spring 1942.

The Hurricane IID mounted two Vickers 40mm S Guns under each wing and kept 2 browning machineguns to aid aiming, these aircraft first flew in combat in North Africa where they were used to great effect, being able to destroy any German tank of the period, the Hurricanes manoeuvrability and stableness were a great asset in ground attack but they were under armoured and thus venerable to ground attack.

Due to combat experience and trials carried out on the guns a series of modifications to improve the guns endurance was carried out towards the end of 1942, this became known as the Mk II version of the gun. Initially each gun carried 12 rounds but later the magazine was modified to carry 15 rounds per gun.

The guns were found to be very accurate, I've seen most books/websites stating a figure of around 30% but this seems to be low, in trials carried out in April 1942 figures of between 53% and 67% was given and in early trials figures of up to 80-100% had been shown, so in combat figures around 30-50% would probably be reasonable. This is much greater than rockets but the fact that virtually any aircraft could be easy modified to carry rockets was a great advantage so by 1943/44 the Hurricane IID was declared obsolete.

Generally a 3lb AP shot was fired by the Vickers S Guns, initially this was not fitted with a tracer but to improve accuracy a tracer was fitted towards the end of 1942. Also High Explosive ammunition was produced from August 1942. A littlejohn adaptor was developed for the Vickers gun but this does not seem to have been adapted.